Field of the Invention
Exemplary embodiments of the present invention relate to a system for controlling an intermediate phase Continuously Variable Valve Timing (CVVT) system; and, to a method of controlling the intermediate phase CVVT system wherein the control stability of the CVVT system is prevented from being reduced, and an engine misfire is prevented from occurring due to a delay in responsiveness, and to a system for embodying the same.
Description of Related Art
To enhance the fuel efficiency of a vehicle, reduce the exhaust gas, increase the low-speed torque and enhance the output of the vehicle, a continuously variable valve timing system or a camshaft phaser system (hereinafter, referred to as a CVVT system) which optimizes and controls the timing of opening or closing the intake and exhaust valves of an engine depending on the RPM of the engine has been developed and used.
Recently, in an effort to improve the performance of such a CVVT system, an intermediate phase continuously variable valve timing system (hereinafter, referred to as an intermediate phase CVVT system), which enhances the responsiveness of a system and expand a cam operating region, was provided.
In the intermediate phase CVVT system, the effect of enhancing the fuel efficiency by reducing a pumping loss due to an increase in overlap of the intake and exhaust valves is further enhanced. Furthermore, an exhaust gas reduction effect is further enhanced by re-combusting combustion gas due to internal exhaust gas recirculation (EGR) through a valve overlap optimization depending on conditions of the engine. In addition, low-speed torque increase and output enhancement effects are further enhanced by increasing the volume efficiency due to optimization in timing of the intake valve depending on conditions of the engine. Therefore, the intermediate phase CVVT system can improve the effects of enhancing the fuel efficiency and reducing the exhaust gas, compared to that of the CVVT system.
To achieve the above-mentioned purposes, in the intermediate phase CVVT system, when a control operation for overcoming a difference between a target cam value and a current cam value is performed, the position of the cam is controlled at an intermediate phase rather than being controlled at the most delayed angle (intake) or the most advanced position (exhaust). Accordingly, the responsiveness of the system is enhanced and the cam operating region can be increased, compared to those of the CVVT system.
The intermediate phase CVVT system can have the effect of enhancing the responsiveness through precise control, but in a region in which the oil temperature and the RPM of the engine are low a delay in responsiveness is caused. Consequently, precise control is impossible.
The delay in responsiveness mainly occurs when the intermediate phase CVVT system is controlled wherein Open Loop Response Time (OLRT) is 100° (crank angle)/sec. The present feature makes the efficiency of emission effect for reducing harmful substances be reduced.
Furthermore, there is a problem in that, when the RPM of the engine is excessively varied, an engine misfire is caused.
Moreover, the intermediate phase CVVT system must comply with regulations in which performance assurance must be satisfied under conditions of an oil temperature range from −10° C. to 130° C. and an engine RPM of 500 RPM or more. Therefore, responsiveness delay which is caused under some certain low-speed and high-temperature conditions may reduce the reliability in performance assurance of the intermediate phase CVVT system.
The foregoing is intended merely to aid in the understanding of the background of the present invention, and is not intended to mean that the present invention falls within the purview of the related art that is already known to those skilled in the art.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.